This nonprovisional application claims priority under 35 U.S.C. xc2xa7119(a) on Patent Application No. 2002-016640 tiled in JAPAN on Jan. 25, 2002, which is herein incorporated by reference.
This invention relates to a method for preparing organopolysiloxanes or MQ resins using water glass as a starting material.
A class of organopolysiloxanes, generally referred to as MQ resins, are well known in the art (see U.S. Pat. Nos. 2,676,182, 2,814,601, 5,391,673, JP-A 63-256628 and JP-A 2001-192453).
MQ resins are characterized in that they contain M units (R3SiO1/2) and Q units (SiO2) in the siloxane chain and they are soluble in toluene and other solvents as opposed to silicone resins containing Q units which are generally insoluble in such solvents. It is described in the above-referred patents that D units (R2SiO) and T units (RSiO3/2) can be introduced into the structure using additional reactants having such units and that monovalent organic groups represented by R can vary over a wide range.
These MQ resins have a film forming ability and compatibility and are widely employed as a major starting material for silicone pressure-sensitive adhesives, cosmetic bases, liquid injection molding materials, and mold release agents and as a strength enhancing component for silicone rubber.
In view of the Q unit-providing source, processes of making MQ resins are generally divided into two processes, water glass process and silicate process. The silicate process is sub-divided into a process starting with silicon tetrachloride and alcohol and a process starting with a commercially available material such as ethyl silicate.
In the recent years, the environmental problem has become of interest. It is very important to control the quality of industrial waste water. The waste water contains organic components which are mostly organic solvents, unreacted reactants, and by-products. It is urgently required to develop a process capable of minimizing the discharge of such valuable components.
In view of the above, the prior art water glass process has the following problems.
(i) Waste water has an increased biochemical oxygen demand (BOD). The use of an alcohol which is well compatible with water entails an increased cost for alcohol recovery.
(ii) M unit charge is in large excess, exacerbating the utilization of starting reactant.
(iii) Siloxane yield is low.
(iv) Reaction proceeds in multiple stages, exacerbating the efficiency of plant utilization.
(v) Product control is difficult due to a difference between charge M/Q and product M/Q.
More particularly, in the prior art process, water serving as a solvent for water glass, a hydrocarbon solvent (e.g., toluene, xylene) serving as a solvent for both the reactant and the silane/siloxane product, and a water-soluble lower alcohol (e.g., ethanol, isopropanol) which is highly compatible with both the solvents are added in large amounts to form a heterogeneous solvent mixture of water/alcohol/hydrocarbon solvent in which Q units are converted to a solvent-soluble MQ resin. Best results are obtained when this reaction is conducted in multiple stages including at least two stages of neutralization reaction of water glass and subsequent MQ conversion reaction. As a consequence, the MQ resin produced is extracted to the side of hydrocarbon solvent (typically toluene) which is incompatible with water. The alcohol used herein enters the water layer which is treated as waste water. This is the reason why waste water has a high BOD value.
An object of the invention is to provide a method for preparing organopolysiloxanes or MQ resins using water glass as a starting reactant while substantially overcoming the above-described problems.
Making research on the solvent which enables reaction while minimizing the amount thereof migrating to the water layer, the inventor has discovered that a specific oxygen-containing solvent has a notable capability and makes it possible to reduce the BOD value of waste water below one tenth of the prior art value. Based on the empirical fact that the molecular weight of MQ resin lowers as the concentration of water glass is reduced, the inventor has discovered that a combination of low concentration water glass with the specific solvent enables simplification from the multi-stage process to a single-stage process and simultaneously overcomes the problem of disagreement between charge M/Q and product M/Q during synthesis that has been believed unsolvable in the prior art. The present invention is predicated on these findings.
Accordingly, the present invention provides a method for preparing an organopolysiloxane by reacting water glass diluted with water to a concentration of 3 to 15% by weight with a triorganohalosilane in the presence of an acid and an oxygen-containing solvent having a solubility of at least 1% by weight in water at room temperature (20xc2x0 C.), but not completely compatible with water, and having a boiling point of up to 220xc2x0 C.